Speeding-Bullet Star Leaves Enormous Streak Across Sky

Jet Propulsion Laboratory News Release

2007 August 15

NASA's Galaxy Evolution Explorer has spotted an amazingly long comet-like tail
behind a star streaking through space at supersonic speeds. The star, named
Mira after the Latin word for "wonderful," has been a favorite of astronomers
for about 400 years. It is a fast-moving, older star called a red giant that
sheds massive amounts of surface material.

The space-based Galaxy Evolution Explorer scanned the popular star during its
ongoing survey of the entire sky in ultraviolet light. Astronomers then noticed
what looked like a comet with a gargantuan tail. In fact, material blowing off
Mira is forming a wake 13 light-years long, or about 20,000 times the average
distance of Pluto from the sun. Nothing like this has ever been seen before
around a star.

"I was shocked when I first saw this completely unexpected, humongous tail
trailing behind a well-known star," said Christopher Martin of the California
Institute of Technology in Pasadena, Calif. "It was amazing how Mira's tail
echoed on vast, interstellar scales the familiar phenomena of a jet's contrail
or a speedboat's turbulent wake." Martin is the principal investigator for the
Galaxy Evolution Explorer, and lead author of a Nature paper appearing today
about the discovery. To view the outlandish star,
visit http://www.nasa.gov/mission_pages/galex/20070815/a.html.

Astronomers say Mira's tail offers a unique opportunity to study how stars like
our sun die and ultimately seed new solar systems. As Mira hurtles along, its
tail sheds carbon, oxygen and other important elements needed for new stars,
planets and possibly even life to form. This tail material, visible now for the
first time, has been released over the past 30,000 years.

"This is an utterly new phenomenon to us, and we are still in the process of
understanding the physics involved," said co-author Mark Seibert of the
Observatories of the Carnegie Institution of Washington in Pasadena. "We hope to
be able to read Mira's tail like a ticker tape to learn about the star's life."

Billions of years ago, Mira was similar to our sun. Over time, it began to swell
into what's called a variable red giant - a pulsating, puffed-up star that
periodically grows bright enough to see with the naked eye. Mira will eventually
eject all of its remaining gas into space, forming a colorful shell called a
planetary nebula. The nebula will fade with time, leaving only the burnt-out
core of the original star, which will then be called a white dwarf.

Compared to other red giants, Mira is traveling unusually fast, possibly due to
gravitational boosts from other passing stars over time. It now plows along at
130 kilometers per second, or 291,000 miles per hour. Racing along with Mira is
a small, distant companion thought to be a white dwarf. The pair, also known as
Mira A (the red giant) and Mira B, orbit slowly around each other as they travel
together in the constellation Cetus 350 light-years from Earth.

In addition to Mira's tail, the Galaxy Evolution Explorer also discovered a bow
shock, a type of buildup of hot gas, in front of the star, and two sinuous
streams of material coming out of the star's front and back. Astronomers think
hot gas in the bow shock is heating up the gas blowing off the star, causing it
to fluoresce with ultraviolet light. This glowing material then swirls around
behind the star, creating a turbulent, tail-like wake. The process is similar to
a speeding boat leaving a choppy wake, or a steam train producing a trail of
smoke.

The fact that Mira's tail only glows with ultraviolet light might explain why
other telescopes have missed it. The Galaxy Evolution Explorer is very sensitive
to ultraviolet light and also has an extremely wide field of view, allowing it
to scan the sky for unusual ultraviolet activity.

"It's amazing to discover such a startlingly large and important feature of an
object that has been known and studied for over 400 years," said James D. Neill
of Caltech. "This is exactly the kind of surprise that comes from a survey
mission like the Galaxy Evolution Explorer."

Caltech leads the Galaxy Evolution Explorer mission and is responsible for
science operations and data analysis. NASA's Jet Propulsion Laboratory, also
in Pasadena, manages the mission and built the science instrument. Caltech
manages JPL for NASA. The mission was developed under NASA's Explorers Program
managed by NASA's Goddard Space Flight Center, Greenbelt, Md. Researchers
sponsored by Yonsei University in South Korea and the Centre National d'Etudes
Spatiales (CNES) in France collaborated on this mission.